Keyer circuit using rectified cut-off bias



May 8, 1962 R. M. DAVIDSON KEYER CIRCUIT USING RECIIFIED CUI-OFF BIAS Filed April 2, 1958 INVENTOR v zZQ//Zflawlswg ATTORNEY spaanse KEYER CIRCUIT UsiNG nacrrrrnn CUT-ora eras Richard M. Davidson, Winston-Salem, N.C., assigner to' Western Electric Company, Incorporated, New York, N.Y., a corporation of New York Filed Apr. 2, 1958, Ser. No. 725,966 7 Claims. (Cl. S28-3l) This invention relates to a keyer circuit and more particularly to a keyer circuit for furnishing an accurately timed output pulse upon the occurrence of a keyed interruption in a continuous tone signal.

The maintenance of a selected grid bias on a thyratron tube to control the tiring thereof is a major problem when the tube is arranged to produce an output pulse upon the 'keyed interruption of a continuous tone signal. The control of the bias on the tube so arranged is susceptible particularly to disturbance by spurious changes in the arnplitude of the tone signal caused by high atmospheric noise, i.e., static or interference from adjacent channel transmissions. Therefore, when a thyratron tube is designed to tire upon interruption of a continuous tone signal, safeguards are necessary to prevent accidental firing of the tube when a Acontinuous tone signal is cancelled briefly by static or other interference.

A limiting and biasing arrangement of crystal diodes is provided by this invention in order to maintain a substantially predetermined bias on a thyratron tube.

The bias maintained on the tube is not affected by increases in amplitude ofthe continuous tone signal brought about, for example, by superimposition of lhigh voltages from lightning or other spurious sources onto the continuous tone signal inasmuch as the limiting and biasing diodes are arranged to shunt to ground voltages more negative than the bias voltage, and the voltages more positive than the bias voltage are blocked from reaching the tube by la pair of diode rectitiers.

An especially efficient safeguard to prevent accidental firing of the tube upon unintended interruption of the tone signal is an RC -filter circuit which not only tends to maintain the bias value below the critical firing potential of the tube during normal reception of the tone signal into the keyer system, but also maintains a bias voltage below the firing potential of the thyratron for a period determined by the time constant of the RC filter whenever the incoming signal is interrupted whether due to static, adjacent channel interference, o-r actual interruption of the signal.

An object of this invention is to provide a new and improved keyer circuit.

Another object is the provision of a new and improved keyer circuit for furnishing an accurately timed output pulse upon the occurrence of a keyed interruption of a continuous tone signal.

In order to attain these and other objectives, and in accordance with the general features of the invention, one embodiment thereof includes a keyer system for the provision of an accurately timed output pulse produced by the interruption of a tone transmitted by radio comprising an input circuit having tone receiving means, an output circuit, and an isolation circuit including rectifying means connecting the input circuit with the output circuit, means connected to the rectifying means to limit the rectifying means to provide a desired potential of rectified energy from the input to the output circuit, and means connected to the output circuit to maintain for a predetermined pev riod a direct current supply to the output circuit upon interruption of the tone.

A complete understanding of the invention may be had from the following detailed description of a specific embodiment thereof when read in conjunction with the aprice pended drawing which represents in diagrammatic form a preferred keyer system.

Referring to the drawing, input terminals llt-1l are designed to receive a carrier wave of tonal frequency which may be transmitted from a remote station. The carrier wave is fed from terminals Sil-ll to a first grid of a twin triode phase inverter tube l2 through a shunt grid leak composed of a capacitor i3 and a resistor 14 nserted in series between ground and the one terminal 11 coupled to the rst grid of tube il?. rI'he anode of the first stage of the phase inverter tube l2 is connected to the positive pole of a direct current supply source l5 through a resistor lo, and the cathode is connected to ground through a resistor 17. The amplified signal voltage appearing on the anode of the first stage is supplied to the grid of the next stage of the tube i2 through a coupling capacitor i8 and a variable resistance provided by a potentiometer i9 which is connected to ground. The anode of the second stage is connected to the positive pole of the source l5 through a resistor 2l., and the cathode is connected through a resistor 22 to ground. The resistors El and Z2 are selected so that sine wave voltages equal in amplitude and in degree phase opposition are developed at points 23 and 24, respectively. The lastmentioned amplitude may be varied by adjusting the setting of the potentiometer i9.

The 180 degree out-of-phase voltages are supplied from points 23 and 24 to the cathodes of diodes 25 and 26, respectively, through coupiing capacitors 27 and 28. The cathodes of diodes 25 and Z6 are connected to ground through resistors 219 and Si; of equal .resistances The diodes 25 and 26 are connected as a full-wave rectifier and are poled to produce a negative bias on the control grid of a thyratron tube 32 which is further provided with a cathode load resistor 33. In addition, a neon indicator tube 34 is connected across the anode of the thyratron tube 32 through a resistor 35 to ground such that when the thyratron tube conducts, the indicator tube 34 illuminates.

Connected between the cathodes of the diodes 25 and 2e are a second pair of diodes 36 and 37 arranged in series opposition. The cathode of the diode 36 is connected to the cathode of the diode 25 and the cathode ofthe diode 37 is connected to the cathode of the diode 26. Connected to the common juncture of the anodes of diodes 36 and 37 is the negative pole of a direct current biasing source, such as battery 38, the positive pole of the battery 38 being grounded. This arrangement of diodes 36 and 37 with battery 3S places a predetermined negative bias on the diodes S6 and 37.

An RC filter circuit consisting of a resistor 39 and a capacitor 4l is shown coupled between the output of the rectifier diodes 2S and 26 and ground. The capacitor 4l of the filter circuit is charged to the peak value of the output of the full-wave rectifier :arrangement of diodes 2.5 and 26. The resistor 39 of the lter circuit and diodes 25 and 26 `are designed to offer a combined impedance which is much higher than the combined impedance presented bythe battery 38 and the diodes 36 and 37. Therelfore, any high level burst of energy which increases the `amplitude of the carrier wave signal introduced into the terminals lll-ll does not affect the bias placed on the tube 32, in that it is shunted to ground through the path dened by diodes 36 and 37 and battery .38. Also, due to the parallel arrangement of the diodes 36 and 37 with the diodes 25 and 26, respectively, the amplitude of the full-wave rectified voltage is limited to the voltage value of the battery 38, as mentioned previously.

Upon the keyed interruption of the input signal into the system for a predetermined time period the output of the diodes 25 and 26 will drop to zero 4and the bias Voltage placed on the grid of the tube will rise to the firing potential of the tube. Accordingly, the tube 32 sharp pulse to trigger associated equipment.

aoagooo will tire in the absence of continuous Wave input energy only after the RC i'ilter circuit ceases to provide a control grid voltage on the tube 32 beyond the critical control grid potential on the grid of the tube 32, which may be at zero Volts; or at a value between zero and a negative three volts, for example. Therefore, since the bias voltage is held to a limited value regardless of upward variations of the input signal, the delay between termination of the input signal and the tiring of the thyratron is determined by the time constant of the RC filter; this Vrepresents a fixed delay and enables accurate determinaf tion of the time during which the incoming signal was interrupted.

The thyratron tube 32 is limited to the production ot va short single pulse by being switched off immediately after the tube 32 conducts by a solenoid-operated lockout relay 4t2. The relay l2 is activated by the output of Y the tube 32 to cause a relay contacter 153, which normally is closed on 'a relay contact 414, to move to a relay contact 45. The tube circuit of the thyratron tube 32. is thus opened `and the tube 32 is rendered quiescent. Also, by

means of the switching arrangement provided, the supply path for the plate potential of the tube 32 is changed from the path of the direct current source l5 to the anode of the tube 32, to a path from the source l5 to ground through a reset key 46 and a resistor 47 in series relation therewith. Thus, to return the tube circuit of the thyratron tube 32 to a potentially conductive condition the reset key 46 is opened, which action deenergizes the solenoid of the relay 42, and the contactor t3 then moves trom the contact d5 to the contact dit on which it normally is closed.

The purpose of the lock-out relay operation when the thyratron is red is two-fold. One purpose is to minimize variations in thyratron characteristics normally -associated with thyratrons under continuous operating conditions. This lock-Out feature limits the thyratron tube 32 operation to a short Vsingle pulse. A second purpose is to require the presence of an incoming signal with resulting bias on the thyratron tube 32 before the tube circuit can be harmed, i.e., attempting to arm the circuit by pushing the reset key te without the presence of an input Y signal on the grid of the tube 32 willV result in immediate thyratron pulsing and lock-out by the relay.

The output pulse from the load resistor 33 of thyratron tube v32 is differentiated by a resistor 52 and a capacitor 49 to produce a sharp positive pulse at the keyer system output terminals l-4S. This pulse may triggerv accurately land positively an associated instrument, such as a timer-recorder, not shown.

To determine the nature of the negative potential output applied to the grid of the thyratron tube 32 a test plug S3 is provided in the output connection of the diodes andk 26, and electrical measurement instruments as vwell as devices which produce a graphic representation of a waveform may be utilized at this point for test purposes. It the potential at the test plug `53 requires a Vchange in amplitude, the potentiometer 19 may be adjusted accordingly, for example, to give a minus three vvolt output from the rectifying diodes 2S and 2o during normal reception of tone.

The present keyer system is designed to recognize the termination of transmitted radio signals and to ignore unintentional interruptions of the said signal due to bursts of static or other noises, and will not be affected by adjacent channel transmissions of interrupted continuous lwave energy or energy transmitted by wireless telegraphy.

The system is incapable of being armed in absence of the desired transmitted signal. -The system has a constant operational delay regardless of variations of input signal Y levels occurring immediately prior to the intentional interruptions of the signal, and, further, at the termination of the incoming signal the system produces a single in practical application, the system should maintain its nominal venergy which are 180 degrees out-of-phase.

l ing and biasing arrangement of diodes 2S, 26 and 36,37,

preferably of crystal type,v to furnish a rectified negative bias for a switching device, such as a thyratron tube 32 which is positioned in an outputV circuit 56. The negative voltage bias is unaected by spurious high level energy such as static which may disturb the input into the system since the limiting and biasing arrangement of the diode pairs will operate to shunt voltages to ground when such voltages are of a value more negative than the desired negative biasing voltage of diodes 2S and 26. The limiting diodes 36, 37 are biased to a negative three volts by the battery 38.

The RC circuit 57 will discharge to the tiring 'potential of tube 32 upon interruption of the radio frequency input energy into the system for a predetermined period of time, for example, more than seven milliseconds, as in this application. Thus, a complete break of the 100,0

'cycle tone for sevenmilliseconds is required before the Vinput tends to prevent accidental tiring of the tube 32 caused by cancellation of the input energy by static, for example, inasmuch as it is not likely that random static will cancel Vseven consecutive cycles ofI the 1000 cycle input energy.

lt is manifest that the invention is not limited to the heretofore described embodiment, and that various modifications thereof may be made within the spirit and scope of the invention.

What is claimed is:

1. A keyer system for production of a controlled output comprising an input circuit; an output circuit; an isolation circuit including rectifying means having cathodesconnected tothe input circuit and anodes connected to the output circuit for producing a full-wave rectified output from an input Wave, a sourceof direct current, and second rectifying means having interconnected anodes connected to a negative terminal of the direct current source and cathodes connected to the cathodes of the rst rectifying means for limiting the rectified output to a desired potential; and means connected in parallel to the output circuit for maintaining for a predetermined period a direct current supply to the output circuit upon interruption of the input wave.

2. A keyer system 4for productionV of a controlled output comprising an input circuit; an output circuit; an isolation circuit including rectifyng means having the cathodes connected to the input circuit and anodes connected to the output circuit for producing a full-wave rectied output from an input Wave, a source of direct current, and a pair of diodes having interconnected anodes connected to the source of direct current and cathodes connected to the cathodes of the rectifying means Afor limiting the rectied output to a desired potential; and means connected to the output circuit for maintaining for a predetermined period a supply of direct current to the output circuit upon interruption of the energy reception by the system. n

3. A keyer system for production of a controlled output comprising an input circuit; an output circuit; an isolation circuit including first rectifying means having cathodes connected to the input circuit and anodes connected to the output circuit for producing a full-Wave rectified output from an input wave, a source of direct current, and

second rectifying means having interconnected :anodes connected to a negative terminal of the direct current source and cathodes connected to the cathodes of the first reetifying means for limiting the rectified output to a desired potential; and an RC filter circuit connected to the output circuit -for maintaining for a predetermined period a supply to the output circuit upon interruption of th input Wave.

4. A keyer system comprising an input circuit including means for splitting an input wave into two paths of energy in 180 degrees out-of-phase relation; an output circuit including a grid-controlled switching device and means for making and breaking the circuitry of the switching device for limiting the output of the device to a short pulse; an isolation circuit including a pair of half-wave rectiiiers connected to the paths of input Wave in difierential relation and poled for producing a full-wave negative potential for bias of the control grid of the switching device, the output of the half-wave rectiers being connected to the grid of the grid-controlled switching device of the output circuit, a source of direct current, and a pair of diodes connected to the source of direct current, the diodes being arranged in opposition and connected to each of the half-Wave rectifiers for limiting the rectified energy output to a desired negative potential; and an RC filter circuit connected to the grid of the switching device positioned in the output circuit for maintaining for a predetermined period a supply of negative direct current to the grid upon interruption of the input wave.

5. A keyer system for the provision of an accurately timed output pulse produced by the interruption of an input signal comprising an input circuit including means for amplifying the input signal, a phase inverter for producing two signals 180 degrees out-of-phase; an isolation circuit including a first pair of diodes connected as a full wave rectifier to the phase inverter and poled for producing a negative voltage, a filter circuit connected to the output of the first pair of diodes having a selected time constant for completely interrupting the input signal for a predetermined time before the negative voltage at the output of the first pair of diodes Will reach a predetermined value, and a second pair of diodes arranged in opposition and connected to the first pair of diodes, a source of direct current connected to the second pair of diodes to bias the potential thereof to the potential of the source of direct current, the second pair of diodes limiting the rectified negative voltage from the rst pair of diodes to the voltage of the source of direct current; and an output circuit including a thyratron having a control grid coupled to the output of the filter circuit so as to operate the thyratron upon cessation of the negative potential produced from the input signal, and a relay connected to the thyratron for opening the thyratron'circuit when the thyratron conducts so that the thyratron conducts only a short positive pulse.

6. A circuit for limiting the magnitude of an output signal comprising an input circuit, an output circuit, a Source of alternating current connected to the input circuit, a first pair of diodes having each cathode thereof respectively connected to the input circuit and each anode thereof respectively connected to the output circuit, a second pair of diodes having cach cathode thereof respectively connected to each cathode of the first pair of diodes and each anode thereof interconnected, a negative source of direct current connected to the common junction of the anodes of the second pair of diodes for biasing said diodes to block signals of a predetermined magnitude and to pass signals of a magnitude greater than said predetermined magnitude, whereby the magnitude of the output signal is limited to said predetermined magnitude.

7. A keyer system for production of a controlled output comprising an input line `for receiving an input wave; a triode tube means having an anode, a cathode, and a control grid; a phase inverter tube connecting said control grid to the input line; a pair of rectifying diodes, each having an anode and a cathode; a first coupling capacitor connected between the anode of the triode tube means and the cathode of a first of the rectifying diodes; a second coupling capacitor connected between the cathode of the triode tube means and the cathode of a second of the rectifying diodes; a pair of limiting diodes having cathodes connected to the cathodes of the rectifying diodes; a source of potential connected to the anodes of the limiting diodes for biasing the limiting diodes away from conduction; and an output circuit connected to the anodes of the rectifying diodes.

References Cited in tbe tile of this patent UNITED STATES PATENTS 1,977,256 Swart Oct. 16, 1934 2,153,202 Nichols Apr. 4, 1939 2,425,667 Berry et al Aug. 12, 1947 2,642,558 Terry June 16, 1953 2,758,205 Lubin Aug. 7, 1956 2,771,576 Mezaros Nov. 20, 1956 2,773,181 Singel Dec. 4, 1956 2,774,930 Bixby Dec. 18, 1956 2,797,261 Polyzou June 25, 1957 2,798,571 Schaelchlin Iuly 9, 1957 2,841,719 Radcliffe July 1, 1958 2,850,703 Vogelsong Sept. 2, 1958 2,916,688 Weir Dec. 8, 1960 2,927,267 Petritz Mar. 1, 1960 OTHER REFERENCES Subcarrier Switch for Microwave Party Line, by Harris Electronics, November 1956, pp. -177.

Pulse and Digital Circuits, 4by Millman and Taub, McGraw-Hill, 1956 (page 119 relied on). 

